Device for Driving Light Emitting Diode Strings

1. A device for driving light emitting diodes, for applying in a backlight module of a liquid crystal display (LCD), the device comprising: a DC-to-DC converter, having a first DC-to-DC converter end and a second DC-to-DC converter end, the second DC-to-DC converter end being coupled to a fixed voltage, the DC-to-DC converter outputting a DC voltage from the first DC-to-DC converter end according to a feedback signal; a light emitting diode (LED) string coupled to the first DC-to-DC converter end; a switch electrically connected to the LED string in series, for allowing the DC voltage to drive the LED string and allowing a DC current to flow through the LED string when the switch is turned on; and a feedback circuit for outputting the feedback signal according to the DC current, the feedback circuit comprising: a current-voltage converter, having a first end and a second end, the first end of the current-voltage converter being coupled to the switch, the second end of the current-voltage converter being coupled to the second DC-to-DC converter end, the DC current flowing through the DC-to-DC converter when the switch is turned on, causing the current-voltage converter to generate a first reference voltage according to the DC current, the first reference voltage being used as the feedback signal; whereby the LED string is lit up to reach a predetermined brightness level when the switch is turned on, and the LED string ceases illumination when the switch is turned off.

2. The device according to claim 1 , wherein the LED string comprises an LED or a plurality of LEDs connected in senes.

3. The device according to claim 1 , wherein the DC-to-DC converter comprises a pulse width modulator for adjusting an output signal of the pulse width modulator according to the feedback signal.

4. The device according to claim 3 , wherein the first reference voltage is generated at the first end of the current-voltage converter and fed back to the pulse width modulator when the DC current flows through the current-voltage converter.

5. The device according to claim 4 , wherein the current-voltage converter comprises a resistor.

6. The device according to claim 4 , further comprising: an amplifier, being connected to the first end of the current-voltage converter and the pulse width modulator, for amplifying the feedback signal and outputting the amplified feedback signal to the pulse width modulator.

7. The device according to claim 1 , wherein the feedback circuit further comprises: a voltage feedback circuit, when the switch is turned off, generating a second reference voltage to be used as the feedback signal according to the DC voltage.

8. The device according to claim 7 , wherein the voltage feedback circuit comprises: a first impedance element, having a first end and a second end, the first end of the first impedance element being coupled to the DC voltage, the second end of the first impedance element being coupled to a node, the node being coupled to the pulse width modulator; and a second impedance element, having a first end and a second end, the first end of the second impedance element being coupled to the node, the second end of the second impedance element being coupled to the fixed voltage, the voltage at the node being the second reference voltage; wherein the second reference voltage being determined by the first reference voltage when the switch is turned on, the second reference voltage is used as the feedback signal by the feedback circuit; wherein the second reference voltage being determined by the first and second impedance elements when the switch is turned off, wherein the second reference voltage is used as the feedback signal by the feedback circuit.

9. The device according to claim 8 , wherein the voltage feedback circuit further comprises a diode, having a positive end and a negative end, the negative end of the diode being coupled to the node, the positive end of the diode being coupled to the first end of the current-voltage converter.

10. The device according to claim 8 , wherein the voltage feedback circuit further comprises a third impedance element, having a first end and a second end, the first end of the third impedance element being coupled to the node, the second end of the third impedance element being coupled to the first end of the current-voltage converter.

11. The device according to claim 7 , wherein the first reference voltage is generated while the DC current flows through the current-voltage converter, the first end of the current-voltage converter being coupled to the pulse width modulator via a diode.

12. The device according to claim 9 , wherein the current-voltage converter comprises a resistor.

13. The device according to claim 9 , further comprising: an amplifier, being connected to the first end of the current-voltage converter and the positive end of the diode, for amplifying and outputting the feedback signal to the pulse width modulator.

14. The device according to claim 1 , wherein the fixed voltage is ground.

15. The device according to claim 1 , wherein the DC-to-DC converter is a Buck converter.

16. The device according to claim 1 , wherein the DC-to-DC converter is a Boost converter.

17. The device according to claim 1 , wherein the DC-to-DC converter is a Buck-Boost converter.

18. The device according to claim 1 , wherein the DC-to-DC converter is a Full-Bridge converter.

19. The device according to claim 1 , wherein the DC-to-DC converter is a Flyback converter.

20. The device according to claim 1 , wherein the driving device for LED strings is for applying in a backlight module of a LCD.

21. The device according to claim 1 , wherein the DC-to-DC converter comprises a comparator for adjusting an output signal of the comparator according to the feedback signal and a reference signal.

22. The device according to claim 21 , wherein the first reference voltage is generated at the first end of the current-voltage converter and fed back to the comparator when the DC current flows through the current-voltage converter.

23. The device according to claim 22 , wherein the current-voltage converter comprises a resistor.

24. The device according to claim 22 , further comprising: an amplifier, being connected to the first end of the current-voltage converter and the comparator, for amplifying the feedback signal and outputting the amplified feedback signal to the comparator.

25. A device for driving light emitting diodes, for applying in a backlight module of a liquid crystal display (LCD), the device comprising: a DC-to-DC converter, having a first DC-to-DC converter end and a second DC-to-DC converter end, the second DC-to-DC converter end being coupled to a fixed voltage, the DC-to-DC converter outputting a DC voltage from the first DC-to-DC converter end according to a feedback signal, the DC-to-DC converter further comprising: a pulse width modulator for adjusting an output signal of the pulse width modulator according to the feedback signal so that the DC-to-DC converter 208 outputs the DC voltage according to the output signal of the pulse width modulator; a light emitting diode (LED) string coupled to the first DC-to-DC converter end; a switch electrically connected to the LED string in series, for allowing the DC voltage to drive the LED string and allowing a DC current to flow through the LED string when the switch is turned on; and a feedback circuit for outputting the feedback signal according to the DC current; whereby the LED string is lit up to reach a predetermined brightness level when the switch is turned on, and the LED string ceases illumination when the switch is turned off.

26. The device according to claim 25 , wherein the feedback circuit comprises: a current-voltage converter, having a first end and a second end, the first end of the current-voltage converter being coupled to the switch, the second end of the current-voltage converter being coupled to the second DC-to-DC converter end, wherein the DC current flows through the current-voltage converter when the switch is turned on, causing the current-voltage converter to generate a first reference voltage as the feedback signal, according to the DC current; and a voltage feedback circuit, when the switch is turned off, generating a second reference voltage to be used as the feedback signal according to the DC voltage.

27. The device according to claim 26 , wherein the first reference voltage is generated while the DC current flows through the current-voltage converter, the first end of the current-voltage converter being coupled to the pulse width modulator via a diode.

28. The device according to claim 26 , wherein the voltage feedback circuit comprises: a first impedance element, having a first end and a second end, the first end of the first impedance element being coupled to the DC voltage, the second end of the first impedance element being coupled to a node, the node being coupled to the pulse width modulator; and a second impedance element, having a first end and a second end, the first end of the second impedance element being coupled to the node, the second end of the second impedance element being coupled to the fixed voltage, the voltage at the node being the second reference voltage; wherein the second reference voltage being determined by the first reference voltage when the switch is turned on, the second reference voltage is used as the feedback signal by the feedback circuit; wherein the second reference voltage being determined by the first and second impedance elements when the switch is turned off, wherein the second reference voltage is used as the feedback signal by the feedback circuit.

29. The device according to claim 28 , wherein the voltage feedback circuit further comprises a third impedance element, having a first end and a second end, the first end of the third impedance element being coupled to the node, the second end of the third impedance element being coupled to the first end of the current-voltage converter.

30. The device according to claim 28 , wherein the voltage feedback circuit further comprises a diode, having a positive end and a negative end, the negative end of the diode being coupled to the node, the positive end of the diode being coupled to the first end of the current-voltage converter.

31. The device according to claim 30 , wherein the current-voltage converter comprises a resistor.

32. The device according to claim 30 , further comprising: an amplifier, being connected to the first end of the current-voltage converter and the positive end of the diode, for amplifying and outputting the feedback signal to the pulse width modulator.

33. The device according to claim 25 , wherein the fixed voltage is ground.

34. The device according to claim 25 , wherein the DC-to-DC converter further comprises a Buck converter.

35. The device according to claim 25 , wherein the DC-to-DC converter further comprises a Boost converter.

36. The device according to claim 25 , wherein the DC-to-DC converter further comprises a Buck-Boost converter.

37. The device according to claim 25 , wherein the DC-to-DC converter further comprises a Full-Bridge converter.

38. The device according to claim 25 , wherein the DC-to-DC converter further comprises a Flyback converter.

39. The device according to claim 25 , wherein the driving device for LED strings is for applying in a backlight module of a LCD.

40. The device according to claim 25 , wherein the pulse width modulator adjusts the output signal of the pulse width modulator according to the feedback signal and a reference signal.

41. The device according to claim 40 , wherein the pulse width modulator comprises a comparator for comparing the output signal of the pulse width modulator according to the feedback signal and a reference signal.